This month, we tame a reflective room, tweak vocal compressors and slay the Blue Screen Of Death.
Roshan Bains writes and records music (mainly hip‑hop), but contacted us because he felt that the quality of his recordings was suffering due to the acoustics of the bare bedroom he was using as a studio. Not only was the room almost an exact square, but it was also devoid of any absorbent surfaces, other than the carpet. He was also experiencing some odd computer problems, and said he would welcome advice on mixing and processing vocals.
Greeted on our arrival by the now customary coffee and chocolate Hob Nobs, we played some of Hugh's test material while measuring the room. Roshan's Behringer Truth B2031 monitors were set up on the shelf of a robust desk that he'd built. The height of the shelf left them aimed slightly high, but otherwise the position was fine. Behind the desk was a bay window, which worried me a little because Roshan's mixing position was right at the focus of the curve, but as luck would have it, low frequencies passed through the double‑glazed units while higher frequencies were attenuated by the heavy velour curtain he'd installed. Our test tracks indicated that the bass end was reasonably even, but the stereo imaging was rather messy, and the whole room sounded over‑live, with distinct flutter echoes between the side walls.
Square rooms are rarely good news for acousticians, but at least this one was a decent size, being 3.5 metres on each side, and fitted cupboards ran along the full length of the left‑hand wall, reducing the width to a little over three metres. These cupboards were just as reflective as the plaster walls, but they did at least provide some impromptu bass trapping, as did the door to the room. As is often the case with square rooms, there was a dramatic drop in bass when standing at the exact centre, but because Roshan's listening position was well forward of that area, this wasn't really a problem for him.
Our solution to the over‑liveness of the room was simple, and made use of six Auralex two‑inch foam panels, with thin strips of wood glued to the back near to one end. The plan was to use self‑adhesive plastic hooks on the wall, then to hang the foam panels by slotting the wooden strip over the hooks. This proved very successful, and saved having to drill the walls or glue foam directly to them. Two panels were hung to the left and right of the mixing position to cover the 'mirror points' (places on the side walls where a mirror would show you an image of your monitors when seated in your normal listening position), and one of these panels had to be hung on a wardrobe door, with a cutout in the foam for the door handle. The hooks failed to stick first time around, so we cleaned the surface to remove any traces of furniture polish (methylated sprit is good for this purpose) and re-stuck them.
Three more panels were hung on the bare rear wall and one more attached to the side wall next to the door. To correct the monitor angle, we used a pair of foam speaker-support pads (kindly provided by The Audio Agency) and Hugh adjusted the included foam wedges to get the monitors pointing down towards Roshan's head when he's at the mix position. Hugh also reset the speaker rear‑panel settings for a flat HF response (they'd been set at ‑2dB). Although minimal, our treatment dramatically reduced the apparent liveness of the room, removed almost all the obvious flutter echo and made the stereo imaging much more precise.
Roshan wanted to record vocals in the same room, but the reflective nature of the space had compromised his results to date, so we installed an SE Reflexion Filter behind his AKG SolidTube microphone, and suggested that he work with the singer's back towards one of the foam panels or, better still, hang a heavy double duvet behind the singer in a 'V' shape, to offer some side as well as rear absorption. A Reflexion Filter reduces the sound getting into the rear and sides of the mic, and also reduces the amount of vocal spilling out into the room to some extent, but you still need to ensure that there are no reflections reaching the mic from behind the singer — which is where the duvet comes in. A nice heavy polyester type (cheap is fine) hung over a pair of microphone boom stands, each set up in a 'T' shape, will do nicely. The more expensive feather duvets are actually less good in this role, because the feathers tend to settle to one end when they're draped in this way.
As usual, Hugh set up the Reflexion Filter hardware in our now 'standard' SOS arrangement (see box below), which improves the stability of the device by bringing its centre of gravity much closer to the centre of the mic stand. We did some speech-recording tests with this setup, and the results sounded acceptably dry. One thing to bear in mind if you try this yourself, though, is that any room coloration that does remain will become more apparent the more you compress the vocal track — so don't skimp on the duvets!
It was during these tests that Roshan's computer problems became very apparent to us. Roshan uses Cubase SX, Pro Tools and Reason, all running on a PAQ PC that's hooked up to a Digidesign Digi 002 audio interface. The computer itself is impressively quiet, so there were none of the noise problems you get with some PCs, but Roshan had recently been experiencing 'Blue Screen Of Death' problems whenever he knocked the PC during operation — and I just happened to close its front panel while he was playing back our test material. Immediately, the computer quit on us, and such behaviour usually means that there's a hardware conflict of some sort, or more probably a bad physical connection somewhere inside.
I suspected the latter to be the case — even though Roshan had been inside the box only a few days earlier, pushing in all the connectors — and as I had a can of Caig's Deoxit on me, I thought that it would be worth treating all the push‑on connectors that I could reach, just in case one of them was suffering from dirty contacts. I managed to access most of the drive and power cables, and we then powered up the computer with the side panel still off, to see if any part of it was more vulnerable to disturbance than any other. Thankfully, after we applied the Deoxit the computer refused to quit, no matter what we did to it, so we replaced the panels and pushed the machine back under the desk.
Roshan also wanted advice on the use of compression and on mixing more generally, and although 'how to mix' is not the sort of thing you can learn in a day, a few simple tips and tricks can go a long way. The first piece of advice we gave him was to compare the balance of his own mixes with that of commercial releases he likes, not only from the mixing position but also while standing outside the studio door on the landing. As many engineers have discovered, listening to a mix from outside the room often reveals balance problems that aren't so apparent when sitting right in front of the speakers. Listening to good commercial material is also a great way to get to know your monitors, and give you a point of reference so you don't lose perspective on your own mix. (For more on this, have a look at Mike Senior's article on compiling a reference CD in SOS September 2008, or at /sos/sep08/articles/referencecd.htm).
Next on the agenda was vocal compression. Roshan was correctly inserting compressors into the vocal track's insert point or, where several vocal tracks were being used, into a subgroup through which the vocals were being submixed. However, he'd simply been inserting compressors and dialling up presets, and although this approach can get you in the right ball-park for attack and release settings, you'll always need to adjust the threshold (or input level, depending on the type of compressor) to suit the material. Otherwise, the gain reduction will kick in at the wrong times, or even not at all. We'd already advised Roshan to leave 10dB or so of headroom when recording any of his audio tracks (an approach that makes overloading the mix output stage less likely), but this meant that the vocal level on his recordings often didn't reach the default compressor threshold setting, and on the examples he showed us, no compression was actually taking place. We gave him a little hands‑on demonstration of how to make better use of his compressors: if you call up a vocal compressor preset, all you really need to do is lower the threshold level until the gain‑reduction meter shows the compressor is pulling the gain down on peaks. The actual amount depends on what's needed and is best judged by ear, but a good ball‑park figure is a maximum 6dB reduction for normal pop songs and perhaps 10 to 12dB of gain reduction for rock or hip‑hop songs, where you need a more up‑front, assertive sound.
Finally, we discussed Roshan's AKG SolidTube mic. This model gives a strong, warm sound, but it isn't as generous with the high end as are some condensers, so we said that if he felt the vocal needed a bit more sizzle, all he need do is dial in a broad, gentle EQ boost at around 10kHz.
Having tidied away all our tools, we left Roshan to try some mixing in his newly treated room. We felt that an application of simple acoustic treatment had made a big subjective difference to the room, and Roshan commented that individual sounds within his mixes were now much easier to pick out.
Roshan: "Thank you very much for taking the time out to visit, and for helping me with my studio problems: it is greatly appreciated. I've noticed a huge difference in the way the room responds to sounds. It is no longer 'clingy' and 'tinny', and the room seems well balanced and natural when I'm mixing. The way you set up the speakers and acoustic treatment has improved the stereo imaging massively, so that I can now pinpoint each instrument in a song a lot more easily. It's like I'm listening to just the speakers without any unwanted acoustics.
You also gave me great advice on recording vocals, and showed me how to compress and EQ them in the way that will best fit my style of music — and now my vocals pierce through the mix and have that 'in your face' property, which is just what I wanted. The SE Reflexion Filter has helped get the dead sound I needed for recording vocals.
"Thanks again to the Studio SOS Team for giving me a mixing and recording space that I can feel confident in. Thanks also to The Audio Agency, Auralex and Sonic Distribution for supplying the speaker pads, acoustic foam and Reflexion Filter.”
We often write in Studio SOS about tweaking the mounting hardware of the SE Reflexion Filter to improve its balance on a mic stand, by shifting the centre of gravity.
From time to time, readers ask if we can explain how to do this in a little more detail. We've already done this, in the shape of a full, illustrated description in the Q&A section of SOS May 2009, or on the SOS web site at /sos/may09/articles/qa0509_2.htm.
Although we'll always look at the acoustics of your recording and mixing spaces in a Studio SOS, we think there's a whole lot more advice that we can give, whether it be about arranging, recording or mixing techniques, and we're always on the lookout for interesting challenges. So if you're need of help — and particularly if you think you have some thorny problems that other readers might be able to learn from — drop us a line at firstname.lastname@example.org. While we're not open to bribery, a promise of a plate of chocolate Hob Nobs never goes unappreciated...